Hari Ji Singh

A computational approach to design energetic ionic liquids

The present work deals with the theoretical estimation of ion-pair binding energies and the energetic properties of four ion pairs formed by combining the 1-butyl-2,4-dinitro-3-methyl imidazolium ion with nitrate (I), perchlorate (II), dinitramide (III), or 3,5-dinitro-1,2,4-triazolate (IV) anions. The counterpoise-corrected ion-pair binding energies were calculated for each ion pair at the B3LYP/6-311+G(d,p) level of theory. Results show that the cation–anion interaction is strongest for ion pair I and weakest for IV, indicating that the nitrate (I) has a greater tendency to exist as a stable ionic salt whereas the 3,5-dinitro-1,2,4-triazolate (IV) may exist as an ionic liquid. Natural bond orbital (NBO) analysis and electrostatic potential (ESP) mapping revealed that charge transfer occurs in all of the ion pairs, but is greatest (0.25e) for ion pair I and smallest (0.03e) for IV, resulting in ion pair I being the least polarized. A nucleus-independent chemical shift (NICS) study revealed that the aromaticity of the 1-butyl-2,4-dinitro-3-methyl imidazolium ion significantly increases in ion pair IV, indicating that this has the greatest charge delocalization among all of the four ion pairs considered. Studies of thermodynamic and detonation properties showed that ion pair II is the most energetic ion pair in terms of its detonation velocity (D = 7.5 km s−1) and detonation pressure (P = 23.1 GPa). It is also envisaged that ion pair IV would exist as an energetic azolium azolate type ionic liquid that could be conveniently used as a secondary explosive characterized by detonation parameters D and P of 6.9 km s−1 and 19.3 GPa, respectively. These values are comparable to those of conventional explosives such as TNT.

Anion directed supramolecular architecture of pyrazole based ionic salts

The reaction of 3,5-diphenylpyrazole (PzPh2H) with different inorganic acids affords salts viz., PzPh2H2+·H2PO4− (1), PzPh2H2+·NO3−·H2O (2), PzPh2H2+·Cl− (3), 8PzPh2H2+·4HSO4−·2SO4−2·3H2O (4) and PzPh2H2+·ClO4−·H2O·CH3OH (5) with different structures. The present study demonstrates that the formation of hydrogen bond between protonated pyrazoles and anions provides a sufficient driving force for the directed assembly of an extensive supramolecular frame work. Theoretical studies reveal that with the increase in the strength of the inorganic acid, the hydrogen bond interaction energy increases. Using Gaussview to analyse the optimized geometries obtained at DFT(B3LYP)/6-31G(d,p) level of theory further revealed that the orientation of molecules remained the same both in the solid and gaseous phases.

Computational study on the kinetics of OH initiated oxidation of methyl difluoroacetate (CF2HCOOCH3)

The kinetics of hydrogen atom abstraction reactions of methyl difluoroacetate (CF2HCOOCH3) by OH radical has been studied by quantum mechanical method. The geometry optimisation and frequency calculation of the titled compound was performed with density functional theory using hybrid meta density functional MPWB1K with 6-31+G(d,p) basis set. Transition states have been determined and intrinsic reaction coordinate (IRC) calculation has been performed to ascertain that the transition from reactants to products was smooth through the corresponding transition state. Energy values are refined by making single point energy calculation at G3B3 level of theory and an energy level diagram is constructed. The standard enthalpies of formation of reactants and other species formed during the reaction were calculated using isodesmic method. The rate constants are calculated using canonical transition state theory and the overall rate constant is determined to be 1.35×10−13 cm3 molecule−1 s−1 at 298 K and 1 atmospheric pressure. Tunnelling has been taken into account in the determination of the rate constant because it plays a critical role at low temperature especially when transfer of hydrogen takes place. The calculated value is found to be in good agreement with the experimentally determined value of 1.48×10−13 cm3 molecule−1 s−1.

Nitro Derivatives of 1,3,5-Triazepine as Potential High-Energy Materials

Structure optimization and frequency calculation of six nitro derivatives of 1,3,5-triazepine were performed using a MP2(FULL)/6-311G(d,p) method. In order to obtain reliable energy data, single-point energy and subsequently thermodynamic properties of the species considered were calculated at a fairly high level of theory, CCSD(T)/6-311G(d,p). Solid-phase heats of formation and crystal density were determined using an electrostatic potential (ESP) method utilizing wave function analysis-surface analysis suite (WFA-SAS) code. The result shows that all nitro derivatives possess high positive heats of formation that increase with an increase in the number of nitro groups attached to the ring moiety. The crystal density was found to be in the range of 1.67–1.90 g/cm3. Detonation properties of the compounds were estimated using the Kamlet-Jacobs equation. The results showed that detonation velocity (D) and detonation pressure (P) increased with an increase in the number of nitro groups attached at the ring moiety. It was found that all six nitro derivatives of the title compound had better or comparable performance characteristics than the most widely used commercial explosives, such as TNT, research and development explosives (RDX), and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). The trinitro derivative (1,3,5-trinitro-1,3,5-triazepine, F) yielded detonation pressure (P) and detonation velocity (D) of 45.5 GPa and 9.23 km/s, respectively, at a loading density of 1.90 g/cm3, which are superior to the most powerful available explosive HMX (P = 39.00 GPa and D = 9.11 km/s). The results obtained during the present study show that the title compounds can be used as promising futuristic high-energy-density materials (HEDMs).

A computational study on kinetics, mechanism and thermochemistry of gas-phase reactions of 3-hydroxy-2-butanone with OH radicals

AbstractTheoretical investigation has been carried out on the kinetics and reaction mechanism of the gas-phase reaction of 3-hydroxy-2-butanone (3H2B) with OH radical using dual-level procedure employing the optimization at DFT(BHandHLYP)/6-311 ++G(d,p) followed by a single-point energy calculation at the CCSD(T)/6-311 ++G(d,p) level of theory. The pre- and post reactive complexes are also validated at entrance and exit channels, respectively. Thus reaction may be proceed via indirect mechanism. The intrinsic reaction coordinate (IRC) calculation has also been performed to confirm the smooth transition from a reactant to product through the respective transition states. The rate coefficients were calculated for the first time over a wide range of temperature (250–450 K) and described by the following expression: kOH = 7.56 × 10−11exp[ −(549.3 ± 11.2)/T] cm3 molecule−1s−1. At 298 K, our calculated rate coefficient 1.20 × 10−11 cm3 molecule−1 s−1 is in good agreement with the experimental results. Our calculation indicates that H-abstraction from α-C-H site of 3H2B is the dominant reaction channel. Using group-balanced isodesmic reactions, the standard enthalpies of formation for 3H2B and radicals generated by hydrogen abstraction are reported for the first time. The branching ratios of the different reaction channels are also determined. Also, the atmospheric lifetime of 3H2B is also calculated to be 1.04 days. Graphical AbstractGas-phase reactions of 3-hydroxy-2-butanone with OH radicals at 298 K were studied.

Computational studies on the thermal decomposition of the CH2FOCHFO radical

Theoretical studies have been carried out on the kinetics and thermochemistry of the thermal decomposition of the CH2FOCHFO radical formed during the photo-oxidation of CH2FOCH2F (HFE-152E) using the dual-level method of obtaining the optimised structure at DFT(M06-2X)/6-311++G(d,p) followed by a single-point energy calculation at the G3 level of theory. The rate constant for different reaction channels involved during the decomposition processes of CH2FOCHFO is evaluated at 298 K and 1 atm using canonical transition-state theory. The results point out that the C–H bond scission is the dominant path involving an energy barrier of 9.5 kcal mol−1 determined at the G3 level of theory. A potential energy diagram is constructed and the results are compared with the data available from the literature for a structurally similar molecule.

Computational study of proton and methyl cation affinities of imidazole-based highly energetic ionic liquids.

The present study deals with the evaluation of gas phase proton and methyl cation affinities for alkyl- and nitrosubstituted imidazoles using DFT (B3LYP)/6-31 + G(d) and MP2 methods in the Gaussian 03 software package. The extent of charge delocalization of these cations is correlated with proton affinity. The study reveals that weakly electron-donating alkyl groups at position 1 of the imidazole enhance its proton affinity, which also increases with increasing alkyl chain length. This is expected to result in an increased tendency to form salts. In contrast, the presence of strongly electron-withdrawing nitro groups lowers proton affinity, which decreases as the number of nitro groups on the ring increases. The same trend is observed for the methyl cation affinity, but to a lower degree. These trends in the proton and methyl cation affinities were analyzed to study the effects of these substituents on the basicity of the energetic imidazole moieties and their tendency to form salts. This, in turn, should aid searches for better highly energetic ionic liquids. In addition, calculations performed on different isomers of mono and dinitroimidazoles show that 5-nitro-1H-imidazole and 2,4-dinitro-1H-imidazole are more stable than the other isomers. Amongst the many nitro derivatives of imidazoles considered in the present study, cations resulting from these two would be the best choice for creating highly energetic ionic liquids when coupled with appropriate energetic anions.

Computational studies on nitramino derivatives of 1-amino-1,2-azaboriridine as high energetic material

In this study, we have applied computational methods to determine the thermodynamic and explosive characteristics of nitramino derivatives of 1-amino-1,2-azaboriridine. Mono-, di- and tri-nitramino derivatives have been designed and considered for detailed study. Structure optimization and frequency calculation of the species have been performed at DFT-B3LYP/6-311++G(d,p) level of theory. The atomization method is employed to calculate the heat of formation (HOF), using electronic energy data calculated at G3 level. Utilizing the WFA program, crystal densities of designed compounds considered during the present study were predicted using the data obtained at B3PW91/6-31G(d,p) level. Results show that the number of nitramino groups influences the heat of formation of the title compounds. The calculated bond dissociation energies suggest that the N–NO2 bond of the nitramino group is the weakest bond and may be treated as a trigger bond involved in the detonation process. The impact sensitivities (h50) of all the compounds were evaluated and it was found that the designed compound 1-amino-2,3,3-trinitramino-1,2-azaboriridine is highly insensitive towards impact. Theoretical estimate of the condensed phase density of nitramino derivatives was found to be in the range of 1.60–1.80 g cm−3. Detonation velocity (D) and the detonation pressure (P) were found to be 8.0–9.0 km s−1 and 26.2–35.2 GPa, respectively. The present investigation reveals that one of the designed compounds 1-amino-2,3,3-trinitramino-1,2-azaboriridine meets the criteria for high energy density materials.

Computational studies on 1,2,4-Triazolium-based salts as energetic materials

AbstractThe results of the computational studies performed on 1,2,4-triazolium cation-based salts designed by pairing it with energetic nitro-substituted 5- membered N-heterocyclic anions such as 5-nitrotetrazolate, 3,5-dinitrotriazolate, and 2,4,5 trinitroimidazolate are reported. Condensed phase heats of formation of the designed ionic salts and their thermodynamic and energetic properties have also been calculated. The results show that these salts are potential energetic materials and possess high positive heats of formation. The detonation velocity, D, and detonation pressure, P, have been calculated using the Kamlet-Jacobs equation and found to be 7–8 km/s and 25–29 GPa, respectively. These values fall in the range of the criteria to designate them as high-energy-density materials. Nucleus independent chemical shift (NICS) studies performed on the designed molecules show that these salts are stable in nature. Graphical AbstractCondensed phase heats of formation of the designed triazolium-based ionic salts and their thermodynamic and energetic properties have been determined using computational methods. The calculated energetic properties indicate that the –NO2 and the –N3 groups are the effective explosophores for enhancing the detonation performance of the substituted triazolium cations.

Computational Studies on Nitro-Azaboriridine—A High-Energetic Material

Nitrogen heterocycles and their derivatives are one of the classes of compounds that have been widely used in developing high-energetic materials. The energy content of the heterocycle ring systems can be increased by inclusion of nitro, cyano, and azido groups. In the present study nitro derivatives of small three-membered B-N-C ring compounds, viz. 1-nitro-1,2-azaboriridine, 1,3-dinitro-1,2-azaboriridine, and 1,3,3-trinitro-1,2-azaboriridine, have been considered. Thermodynamic properties and energetics of the above compounds have been taken for detailed computational study using G2, G3, and CBSQB3 compound methods. Studies reveal that these compounds can be considered for use as high-energetic materials. Detonation velocity (D) and detonation pressure (P) of the title compounds have also been evaluated using the Kamlet-Jacobs method based on the theoretical densities and heats of formation calculated at G3 level. Calculation shows that 1,3,3-trinitro-1,2-azaboriridine yields a detonation velocity of 9.14 km/s and a detonation pressure of 40.2 GPa at a loading density of 1.91 g/cm3 that is comparable to powerful commercial explosives such as HMX (9.10 km/s, 1.91 g/cm3, 39.0 GPa) and RDX (8.75 km/s, 1.82 g/cm3, 34.0 GPa).